Improved situational awareness is increasingly required for many applications including surveillance systems, videoconference vision systems, and vehicle vision systems. Essential to such applications is the need to monitor a wide operating area and to form a composite image for easy comprehension in different user modes. To minimize the number of cameras and cost, cameras with panoramic lens enable a wide field of view but will have distortions due to inherent geometric shape and optical non-linearity. In a surveillance application, multiple panoramic cameras may cover the entire exterior and interior area of a building, and the system can provide continuous view of the area and, manually or automatically, track objects through the area.
In a vehicle vision system, multiple panoramic cameras can provide a full 360° view of the area and around obstructive objects. Such systems can adapt display views to specific operator modes such as turning, reversing, and lane changing to improve situational awareness. Additional advantages of a vehicle vision system are reducing the wind drag and noise caused by side mirrors, and reducing the width span of the vehicle by eliminating such protruding mirrors. These systems can also have the capability to detect objects in motion, provide warning of close objects, and track such objects through multiple viewing regions. Vision systems could also greatly enhance night vision through various technologies such as infrared, radar, and light sensitive devices.
Vision systems consist of one or more image acquisition devices, coupled to one or more viewable display units. An image acquisition device can incorporate different lenses with different focal lengths and depths of focus such as planar, panoramic, fish-eye, and annular. Lenses like fish-eye and annular have a wide field of view and a large depth of focus. They can capture a wide and deep field of view. They tend, however, to distort images, especially the edges. Resulting images look disproportionate. In any type of lens, there are also optical distortions caused by tangential and radial lens imperfections, lens offset, focal length of the lens, and light falloff near the outer portions of the lens. In a vision system, there are yet other types of image distortions caused by luminance variations and color aberrations. These distortions affect the quality and sharpness of the image.
Prior art panoramic vision systems do not remove image distortions while accurately blending multiple images. One such panoramic system is disclosed in U.S. Pat. No. 6,498,620B2, namely a rearview vision system for a vehicle. This system consists of image capture devices, an image synthesizer, and a display system. Neither in this document, nor in the ones referenced therein, is there an electronic image processing system correcting for geometric, optical, color aberration, and luminance image distortions. In the United States Patent Application Publication No. 2003/0103141A1 a vehicle vision system includes pre-calibration based luminance correction only but not other optical and geometric corrections. A thorough luminance and chrominance correction should be based on input and output optical and geometric parameters and be adaptive for changing ambient environments.
Distorted images and discontinuity between multiple images slow down the operator's visual cognizance, and as such, her/his situational awareness, resulting in potential errors. This is one of the most important impediments in launching an efficient panoramic vision system. It is therefore desirable to provide a panoramic vision system with accurate representation of the situational view via removing geometric, optical, color aberration, luminance, and other image distortions and providing a composite image of multiple views. Such corrections will aid visualization and recognition and will improve visual image quality.